Curable and optically clear pressure sensitive adhesive and uses thereof

ABSTRACT

Curable silicone pressure sensitive adhesive compositions and films suitable for sealing and adhering substrates for optically clear electronic devices are described. The curable silicone pressure sensitive adhesive compositions are suitable as films or encapsulants for adhering electronic devices, e.g., LCD display, LED display, flexible display, touch screen, and flexible thin film photovoltaic module.

FIELD OF THE INVENTION

The invention relates to curable, optically clear, pressure sensitiveadhesives. The optically clear adhesives are suitable as films,laminants, tapes or encapsulants for adhering electronic devices, e.g.,LCD display, LED display, flexible and foldable display, touch screen,and flexible thin film photovoltaic module.

BACKGROUND OF THE INVENTION

Electronic devices and circuits generally made of an active layer inbetween a cover front sheet and a substrate back sheet. At least one ofthe sheets is optically transparent. The substrate and cover sheets areadhered together with a laminating adhesive film that enhances lighttransmission and optical clarity. Desirably, the adhesive maintainsadhesion for the substrates in a wide range of temperatures.

Adhesives in the form of laminating films improve handleability overliquid-based adhesive; however, there are several drawbacks tofilm-based adhesive. Films have poor substrate wet-out and poor voidfilling during the assembly process, and this problem is exacerbated forsubstrates that contain indentations and cavities created by componentson substrates such as, electrodes, bus bars, ink steps, and integratedcircuits.

WO2009148722 and WO2011062932 references describe polyisobutylene-basedfilm adhesives with a relatively high viscosity. In order to obtain abetter wet out, the film adhesive is applied onto the substrate underhot lamination. However, many active organic and electronic componentsare sensitive to heat above 60° C., and prolonged exposure to such highheat results in detrimental effects on the electronic components.

JP2012057065 reference discloses non-curable pressure sensitive adhesivefilms. In order to properly wet-out the substrates and to minimize voidformations, the viscosity of the adhesive film is kept below 1,000,000cps or below 200,000 g/mol viscosity average molecular weight (Mv) at120° C.; however, the uncured thermal plastic adhesive exhibits coldflow under strain during the lifetime of the device. Similarly,CN104130740 reference teaches an organosilicone pressure sensitiveadhesive film with high stripping force. Again, the film is notUV-curable, and exhibits cold flow under stain during the lifetime ofthe device.

CN 103820042 reference discloses the use of SIS and SBS block copolymerto make a film-based, heat-curable, hot melt adhesive for thermal-meltoptical clear adhesive (TOCA). The unsaturated C═C functional bonds inthe soft block of SIS and SBS block copolymer readily oxidizes in airunder UV light or at elevated temperature, and the adhesive filmdiscolors to yellow or brown over time, compromising optical clarity.

WO2013173976A1 reference discloses another challenge known as “Mura” foroptical devices. Mura is defined as appearance of dark spots and patcheson optical devices, caused by uneven screen uniformity or a localizedstress. Any kind of stress, even at low levels, inside the adhesivelayer can cause Mura and this is not a repairable defect for opticaldevices. Pressure sensitive adhesives with low modulus (soft) isdesirable to overcome the Mura.

Hydrogels have also been used as adhesive film layer for electronicdevices. U.S. Pat. Nos. 5,559,165 and 6,448,303 references disclose softadhesives that leave no oil residue upon removal from a hard substrate.EP175562 reference describes electron-beam curable hydrogel-like softadhesives. Similarly, U.S. Pat. No. 5,262,468 reference describes theuse of high viscosity rubbers (40,000 cp at 25 wt % in toluene) toobtain gelatinous thermoplastic compositions. While all of thesecompositions are soft and pliable, they lack adhesive adhesion and failto adhere to substrates.

Pressure sensitive adhesives with a balanced low modulus and balancedpeel adhesion are desirable to overcome the Mura problem anddelamination problem. It is also desirable for the pressure sensitiveadhesive to have a wide temperature use range.

Therefore, there is a need in the art for pressure sensitive adhesivefilm in electronic devices with high optical clarity over prolongedtime, wide temperature usage, high peel adhesion and low modulus aftercure. The current invention fulfills this need.

BRIEF SUMMARY OF THE INVENTION

The invention provides curable silicone pressure sensitive adhesivecompositions and films suitable for sealing and adhering substrates forelectronic devices. The cured film enhances light transmission andoptical effects for a prolonged time in a wide range of temperatures;provide high adhesion, low Mura and modulus.

One aspect of the invention is directed to a curable silicone pressuresensitive adhesive composition comprising a mixture of:

-   -   (a) about 10 to about 98% of a reaction product of:        -   (i) a reactive polydimethylsiloxane polymer, which is a            polydimethylsiloxane polymer α,ω-endcapped with a functional            group;        -   (ii) a reactive silicone resin; and        -   (iii) an acid or a base catalyst that has a pKa value equal            to or less than −6 or equal to or greater than 15;    -   (b) about 1 to about 45% of a (meth)acrylate functionalized        polydimethylsiloxane polymer or oligomer;    -   (c) about 1 to about 45% of a silicone resin or a        polydimethylsiloxane polymer or oligomer; and    -   (d) 0.001-5% of a radical initiator.        The cured adhesive has a transmittance of greater than 90%        measured in accordance with ASTM E903 at 500 nm.

Another aspect of the invention is directed to a curable siliconepressure sensitive adhesive composition comprising a mixture of:

-   -   (a) about 95 to about 99.999% of a reaction product in an        organic solvent of:        -   (i) a reactive polydimethylsiloxane polymer;        -   (ii) a reactive silicone resin;        -   (iii) a (meth)acrylate and/or methoxyl functionalized            polydimethylsiloxane polymer or oligomer; and        -   (iv) an acid or a base catalyst that has a pKa value equal            to or less than −6 or equal to or greater than 15;    -   (b) about 0.001 to about 5% of a radical initiator; and    -   (c) optionally, up to 45% of a silicon resin or a        polydimethylsiloxane polymer or oligomer.        The cured adhesive has a transmittance, measured in accordance        with ASTM E903 at 500 nm, of greater than 90%.

Yet another aspect of the invention is directed to a method of forming acurable silicone pressure sensitive adhesive film comprising the stepsof:

(1) preparing a reaction product of (i) a reactive polydimethylsiloxanepolymer, which is a polydimethylsiloxane α,ω-endcapped with a functionalgroup, (ii) a reactive silicone resin; and (iii) an acid or a basecatalyst in an organic solvent to form a non-curable silicon network;and

(2) combining the non-curable silicon network with (iv) about 5 to about45% of a (meth)acrylate terminated polydimethylsiloxane polymer oroligomer, (v) 5-45% of a silicone resin; (vi) about 0.001 to about 5% ofa radical initiator, and (vii) optionally, a polydimethylsiloxanepolymer or oligomer having a weight average molecular weight of lessthan about 50,000 to form a solution in an organic solvent;

(3) preparing a first release-liner;

(4) coating the solution onto the first release-liner;

(5) let the organic solvent evaporate from the coated film on the firstrelease-liner to form a substantially solvent-free film; and

(6) laminating a second release-liner onto the substantiallysolvent-free film.

In a further aspect of the invention is directed to a method of formingan electronic device comprising the steps of:

(1) making the curable silicone pressure sensitive adhesive filmprepared by combining a reaction product of (i) a reactivepolydimethylsiloxane polymer (ii) a reactive silicone resin; and (iii)an acid or a base catalyst in an organic solvent with (iv) a(meth)acrylate terminated polydimethylsiloxane polymer or oligomer; (v)a silicone resin; and (vi) a radical initiator,

(2) coating the film in between two release liners;

(3) preparing a first substrate, wherein the substrate can be a frontcover sheet or a back substrate of the device;

(4) removing one of the release-liner;

(5) laminating the curable silicone pressure sensitive adhesive filmonto the device substrate at a pressure of about 0.01 to about 0.5 MPa;

(6) removing the other release-liner;

(7) laminating the curable silicone pressure sensitive adhesive filmonto the a second device substrate at a pressure of about 0.01 to about0.5 MPa; and/or a vacuum of about 0.01 to about 0.1 MPa, and/or at atemperature of about 30 to 80° C.;

(8) curing the curable silicone pressure sensitive adhesive film with adosage of UVA&V 1-5 J/cm², and/or heat at 80-150° C.;

whereby the adhesive film adheres onto the first device and the seconddevice substrates.

In another aspect of the invention is directed to a method of forming anelectronic device comprising the steps of:

(1) making the curable silicone pressure sensitive adhesive filmprepared by combining a reaction product of (i) a reactivepolydimethylsiloxane polymer; (ii) a reactive silicone resin; (iii) a(meth)acrylate terminated polydimethylsiloxane polymer or oligomer; and(iv) an acid or a base catalyst in an organic solvent with (v) a radicalinitiator, and optionally (vi) a silicon resin or a polydimethylsiloxanepolymer or oligomer;

(2) coating the film in between two release liners.

(3) preparing a first substrate, wherein the substrate can be a frontcover sheet or a back substrate of the device;

(4) removing one of the release-liner;

(5) laminating the curable silicone pressure sensitive adhesive filmonto the device substrate at a pressure of about 0.01 to about 0.5 MPa;

(6) removing the other release-liner;

(7) laminating the curable silicone pressure sensitive adhesive filmonto the a second device substrate at a pressure of about 0.01 to about0.5 MPa; and/or a vacuum of about 0.01 to about 0.1 MPa, and/or at atemperature of about 30 to 80° C.;

(8) curing the curable silicone pressure sensitive adhesive film with adosage of UVA&V 1-5 J/cm², and/or heat at 80-150° C.;

whereby the adhesive film adheres onto the first device and the seconddevice substrates.

Yet in another aspect of the invention is directed to a method offorming an electronic device comprising the steps of:

(1) making the curable silicone pressure sensitive adhesive filmprepared by combining a reaction product of (i) a reactivepolydimethylsiloxane polymer; (ii) a reactive silicone resin; and (iii)an acid or a base catalyst in an organic solvent with (iv) a(meth)acrylate terminated polydimethylsiloxane polymer or oligomer; (v)a silicone resin; and (vi) a radical initiator;

(2) coating the film in between two release liners;

(3) curing the curable silicone pressure sensitive adhesive film betweenthe two release liners, with a dosage of UVA&V 1-5 J/cm², and/or heat at80-150° C.; whereby the adhesive film adheres onto the first device andthe second device substrates;

(4) preparing a first substrate, wherein the substrate can be a frontcover sheet or a back substrate of the device;

(5) removing one of the release-liner;

(6) laminating the curable silicone pressure sensitive adhesive filmonto the device substrate at a pressure of about 0.01 to about 0.5 MPa;

(7) removing the other release-liner;

(8) laminating the curable silicone pressure sensitive adhesive filmonto the a second device substrate at a pressure of about 0.01 to about0.5 MPa; and/or a vacuum of about 0.01 to about 0.1 MPa, and/or at atemperature of about 30 to 80° C.

In another aspect of the invention is directed to a method of forming anelectronic device comprising the steps of:

(1) making the curable silicone pressure sensitive adhesive filmprepared by combining a reaction product of making the curable siliconepressure sensitive adhesive film prepared by combining a reactionproduct of (i) a reactive polydimethylsiloxane polymer; (ii) a reactivesilicone resin; (iii) a (meth)acrylate terminated polydimethylsiloxanepolymer or oligomer; and (iv) an acid or a base catalyst in an organicsolvent with (v) a radical initiator; and optionally (vi) a siliconresin or a polydimethylsiloxane polymer or oligomer;

(2) coating the film in between two release liners;

(3) curing the curable silicone pressure sensitive adhesive film betweenthe two release liners, with a dosage of UVA&V 1-5 J/cm², and/or heat at80-150° C.; whereby the adhesive film adheres onto the first device andthe second device substrates;

(4) preparing a first substrate, wherein the substrate can be a frontcover sheet or a back substrate of the device;

(5) removing one of the release-liner;

(6) laminating the curable silicone pressure sensitive adhesive filmonto the device substrate at a pressure of about 0.01 to about 0.5 MPa;

(7) removing the other release-liner;

(8) laminating the curable silicone pressure sensitive adhesive filmonto the a second device substrate at a pressure of about 0.01 to about0.5 MPa; and/or a vacuum of about 0.01 to about 0.1 MPa, and/or at atemperature of about 30 to 80° C.

These and other aspects of the invention are described in the detaileddescription below. In no event should the above summary be construed asa limitation on the claimed subject matter which is defined solely bythe claimed as set forth herein.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows RDA Temperature Sweep (modulus curve verses temperature atStrain <30%, 10 rad/s) of cured silicone pressure sensitive adhesivefilms.

DETAILED DESCRIPTION OF THE INVENTION

All documents cited herein are incorporated in their entireties byreference.

Percent, unless expressly stated otherwise, means dry solid weightpercent based on the total weight of the components.

As used herein, an “oligomer” is a molecular complex that consists of atleast two monomer units but less than the number of units of a polymer.

As used herein, a “polymer” is a molecular complex that consists ofmonomer units greater than about 15 monomer units.

As used herein, the term “optically clear” or “optical clarity” refersto transmission of a film of 90% or greater measured in accordance withASTM E903 at 500 nm.

As used herein, the terms “optically clear adhesive,” and “OCA,” usedinterchangeably, refer to adhesive that has optical clarity.

As used herein, the terms “device” and “electronic device,” usedinterchangeably, refer to an article that has various components suchas, circuits or active layers in between a cover front sheet and asubstrate back sheet, and operates by manipulating the flow ofelectrons, e.g., displays, including flexible and foldable displays,outdoor displays, LCD displays, LED displays; diffusers; rigidcompensators; heaters; flexible polarizers; touchscreens; flexible thinfilm photovoltaic cells; mobile phone; tablet PC; TV; notebook PC;digital camera; photo frame; car navigation; and the like.

As used herein, the terms “film,” “tape,” and “encapsulants” usedinterchangeably, refer to an adhesive in a free-standing form thatadhere the components and/or substrates together in the devices.

As used herein, the terms “reactive” refer to a molecule's ability tohydrolyze in the presence of an acid or a base catalyst.

As used herein, the terms “pressure sensitive adhesive” or “PSA,” usedinterchangeably, refer to a viscoelastic material which adheresinstantaneously to most substrates with an application of slightpressure and remains permanently tacky.

As used herein, the terms “polydimethylsiloxane” or “PDMS” usedinterchangeably, refer to a dimethyl substituted polysiloxane.

As used herein, the terms “(meth)acrylate functionalizedpolydimethylsiloxane, “(meth)acrylate functionalized PDMS” or “PDMS-DA”used interchangeably, refer to a dimethyl substituted polysiloxane, withα,ω-endcapped (meth)acrylate functional groups.

The invention provides an optically clear, curable, silicone-basedpressure sensitive adhesive composition. The curable silicone pressuresensitive adhesive composition comprises (a) about 10 to about 98% of areaction product, (b) about 1 to about 45% of a (meth)acrylatefunctionalized polydimethylsiloxane polymer or oligomer, (c) about 1 toabout 45% of a silicone resin or a polydimethylsiloxane polymer oroligomer, and (d) about 0.001 to about 5% of a radical initiator. Thereaction product (a) comprises (i) a reactive polydimethylsiloxanepolymer, which is a polydimethylsiloxane polymer α,ω-endcapped with afunctional group, (ii) a reactive silicone resin; and (iii) an acid or abase catalyst that has a pKa value equal to or less than −6 or equal toor greater than 15. The cured adhesive has a transmittance of greaterthan 90% measured in accordance with ASTM E903 at 500 nm. In anotherembodiment, the optically clear, curable, silicon based pressuresensitive adhesive comprises (a) about 95 about 99.999% of a reactionproduct in an organic solvent of: (i) a reactive polydimethylsiloxanepolymer, (ii) a reactive silicone resin, (iii) a (meth)acrylate andmethoxyl functionalized polydimethylsiloxane polymer or oligomer; and(iv) an acid or a base catalyst that has a pKa value equal to or lessthan −6 or equal to or greater than 15; (b) about 0.001 to about 5% of aradical initiator; and (c) optionally, up to 45% of a silicon resin or apolydimethylsiloxane polymer or oligomer. The cured adhesive has atransmittance, measured in accordance with ASTM E903 at 500 nm, ofgreater than 90%.

The reaction between the reactive polydimethylsiloxane and the reactivesilicone resin occurs at the α,ω-endcaps of the polydimethylsiloxanesite and at the functionalized silicone resin site in the presence ofthe catalyst in the organic solvent. The ratio of the reactivepolydimethylsiloxane polymer or oligomer to the reactive silicone rangesfrom 1:9 to 9:1. The reaction product is a lightly covalentlycross-linked network between the polydimethylsiloxane and the siliconeresin, and yet this network remains soluble in organic solvent.

The weight average molecular weight (Mw) of reactive α,ω-endcappedpolydimethylsiloxane is from about 100 to about 1,000,000 g/mol,preferably, from about 400 to about 350,000 g/mol. The reactivepolydimethylsiloxane polymer is preferably end-capped with reactivegroup such as hydroxyl and/or alkoxy, groups. Other α,ω-endcappedpolydimethylsiloxane, such as diorganosiloxane polymers, can be used.Other diorgano substituents include, for example, methylvinyl,methylphenyl, diphenyl, methylethyl, and 3,3,3-trifluoropropylmethyl. Ina preferred embodiment, the diorgano substitutes are all dimethylsubstituents (PDMS).

A reactive silicone resin is a network of silicone polymer that containsa combination of R₃SiO_(1/2) (M unit), R₂SiO_(2/2) (D unit), RSiO_(3/2)(T unit) and/or SiO_(4/2) (Q unit) in the cage-like chemical Si—O—Sistructure. It can be made according to procedures in U.S. Pat. Nos.2,676,182, 2,814,601 and is also obtained from various commercialsources. Preferred functionalized silicone resin is a silicone resinhaving both M unit and Q unit, also known as MQ resin. Useful reactiveMQ silicone resins in the invention include silicone resins that contain0.05 to 5 weight percent of silicone-bound hydroxyl group and furthercomprise M and Q units in a mole ratio of from 0.5˜1.5 M units for eachQ. The MQ resin is soluble in toluene, xylene, heptane, and the like.Preferred R groups of the M unit in MQ resin are methyl and hydroxyl.The mole ratio of SiO_(4/2) (Q unit) to R₃SiO_(1/2) (M unit) ranges from1:2 to 2:1. One preferred R group is a combination of hydroxyl andmethyl groups, with 0.001 to 1 Si—OH for each Si-Me. The preferred MQresin has a weight average molecular weight of the functionalizedsilicone resin is from about 500 to about 200,000 g/mol.

Useful catalysts can be any acid, or base, and mixtures thereof.Preferred catalysts have a pKa value that has a pKa value equal to orless than −6 or equal to or greater than 15 in a hydrocarbon solvent.Examples of the preferred catalyst are KOH, NaOH, LiOH, organolithiumreagents, Grignard reagents, methanesulfonic acid, sulfuric acid, andmixtures thereof. Other examples of the catalyst include organometallicsalts of metals such as tin, titanium, aluminum, bismuth. Combination ofmore than one type of catalysts above can also be used.

The reaction to form the non-curable silicone product is conducted in anorganic solvent or co-solvents, selected from the aliphatichydrocarbons, aromatic hydrocarbons, diethyl ethers, tetrahydrofurane,ketones, acetates, water and mixtures thereof. Preferred solventsinclude xylene, toluene, heptane, tetrahydrofuran, and mixtures thereof.

Reaction of the reactive PDMS polymer and reactive MQ silicone resin maytake place at room temperature or at an elevated temperatures or up toabout 160° C. The preferred temperature is in the range of 60-150° C.Typically the reaction is from about 1 to about 24 hours. Heating can becontinued until the desired physical properties such as T-peel adhesionor modulus are achieved for the reaction product. The solid content ofthe reaction is from about 20 to 80%, and can be adjusted by adding orremoving solvent.

About 10 to about 98% of the above reaction product is then combined tothe rest of components to form an optically clear pressure sensitiveadhesive. One component is a polydimethylsiloxane polymer or oligomercontaining free radical reactive functional groups. Preferably, thefunctional PDMS (i) has a weight average molecular weight (Mw) of fromabout 400 to about 350,000 g/mol and (ii) contains at least one freeradical reactive functional group per polymer or oligomer chain. Onepreferred functional PDMS is a (meth)acrylate functionalized PDMSpolymer or oligomer. Preferably about 1 to about 45% of the(meth)acrylate functionalized PDMS polymer or oligomer is added to thereaction product to form the curable silicone pressure sensitiveadhesive composition.

The functional group for the PDMS polymer or oligomer is preferablyselected from terminal methacrylates, pendant methacrylates, terminalacrylates, /or pendant acrylates. Examples of siloxane (meth)acrylicoligomers or macromers include polydimethylsiloxane mono (meth)acrylate,e.g. trialkoxylsilyl (meth)acrylates, dialkoxysilyl (meth)acrylates ormethacrylates. Preferred siloxane (meth)acrylic macromers aretrimethoxylsilyl and dimethoxymethylsilyl functional PDMS-acrylate ormethacrylates. The siloxane (meth)acrylic macromer is in the content ofabout 0.2 to 50 weight percent based on the total weight of(meth)acrylic monomers. The amount of polysiloxane-containing(meth)acrylic macromer will typically be used in amounts of from 0.2 to50 weight percent, more preferably, 1 to 15 weight percent of theacrylic polymer. Exemplary functional PDMS polymers or oligomersinclude, but are not limited to, di(meth)acrylated-polydimethylsiloxane, silquiloxane, silane monomers, from Gelest, etc. Aparticularly preferred functional PDMS is methacryloxypropyldimethoxyterminated PDMS made by Henkel Corporation, as described in U.S. Pat.No. 5,300,608.

Other acrylic polymer that can advantageously be used as the functionalgroup in the reactive functional PDMS are acrylic polymers comprisingend-capped alkoxysilyl functional groups or polysiloxane-blocked orgrafted copolymers. Examples of the end-capped alkoxysilyl functionalgroups are trialkoxylsilyl, dialkoxysilyl functional groups. Preferredend-capped alkoxysilyl functional groups are trimethoxylsilyl,dimethoxymethylsilyl, triethoxylsilyl and/or diethoxymethylsilylfunctional groups. Examples of such polymers are MS-polymer from Kaneka.Block copolymers are also useful. An example of a polysiloxane blockcopolymer is polydimethylsiloxane-acrylic block copolymer. The preferredamount of siloxane block is 10 to 50 weight percent of the whole blockpolymer.

The optically clear pressure sensitive adhesive further comprises asilicone resin or a polydimethylsiloxane polymer or oligomer. Thesilicone resin or the polydimethylsiloxane polymer or oligomer ispresent at a level of about 1 to up to about 45%.

The silicone resin can be the same MQ resin as is previously used toform described above in the reaction product between (meth)acrylatefunctionalized PDMS and the silicone resin. Other preferred silicone MQresins contains vinyl, phenyl, (meth)acryloxy, and mixtures thereof inthe M units. The silicone MQ resins can be also further treated withMe₃SiOSiMe₃, ViMe₂SiOSiMe₂Vi, MeViPhSiOSiPhViMe, Me₃SiNHSiMe₃ ortriorganosilane such as Me₃SiCl, Me₂ViSiCl or MeViPhSiCl to reduce theamount of Si—OH in the silicone resin. The mole ratio of SiO_(4/2) (Qunit) to R₃SiO_(1/2) (M unit) ranges from 1:2 to 2:1. The preferredsilicone resin has a weight average molecular weight of thefunctionalized silicone resin is from about 500 to 200,000 g/mol. Thecurable silicone pressure sensitive adhesive composition comprises about1 to about 45% of the silicone resin.

The polydimethylsiloxane polymer or oligomer may be the same PDMS aspreviously described to form the reaction product between PDMS and thesilicone resin or a non-reactive PDMS polymer or oligomer. Otherpreferred polydimethylsiloxane polymer or oligomer contains methyl,vinyl, epoxy, alkoxyl end capped groups to improve adhesion or o havedual cure properties. Yet other preferred polydimethylsiloxane polymeror oligomer is a block copolymer of polydimethylsiloxane with polyimide,polyester, polyether, polyethylene glycol, polypropylene glycol, whichis compatible to the curable adhesive and provides adhesion to varioussubstrates. In one embodiment, the PDMS polymer or oligomer isα,ω-endcapped with methyl, hydroxyl, hydride, vinyl, (meth)acryloxygroups. The polydimethylsiloxane polymer or oligomer has a weightaverage molecular weight (Mw) of from about 400 to 350,000 g/mol.

The pressure sensitive adhesive further comprises a radical initiatorthat generates free radicals and cures the adhesive by radiation cure orby heat cure. The term radiation cure herein refers to crosslinking,toughening, hardening or vulcanization of the curable portion of theadhesives through actinic radiation exposure. Actinic radiation iselectromagnetic radiation that induces a chemical change in a material,including electron-beam curing. In most cases, such radiation isultraviolet (UV) or visible light. The initiation of radiation cure isachieved through the addition of an appropriate photoinitiator. The cureof the adhesive is achieved by direct exposure to ultraviolet (UV) orvisible light or by indirect exposure through transparent cover sheetthat are made of polyester, polycarbonate, glass, and the like.

The selection of a photoinitiator for the radiation curable adhesive isfamiliar to those skilled in the art of radiation and heat cure, and ishighly dependent on the specific applications in which the adhesives areto be used. The photoinitiator is a UV cleavable phtoinitiator, and maycomprise one or more types of photoinitiator and optionally one or morephotosensitizers. Radical photopolymerization initiating systemcomprising one or more photoinitiators and photosensitizers can be foundin Fouassier, J-P., Photoinitiation, Photopolymerization and PhotocuringFundamentals and Applications 1995, Hanser/Gardner Publications, Inc.,New York, N.Y. Suitable radical photoinitiators include Type I alphacleavage initiators such as acetophenone derivatives such as2-hydroxy-2-methylpropiophenone and 1-hydroxycyclohexyl phenyl ketone;acylphosphine oxide derivatives such as bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide; and benzoin ether derivatives such as benzoinmethyl ether and benzoin ethyl ether. Type II photointiators are alsosuitable for the curable adhesive, and they include benzophenone,isopropylthioxanthone, and anthroquinone. Many substituted derivativesof the aforementioned compounds may also be used.

A suitable photoinitiator is one that exhibits a light absorptionspectrum that is distinct from that of the resins, and other additivesin the adhesive. The amount of the photoinitiator is typically is in arange of about 0.001 to about 10 parts, preferably, from about 0.01 toabout 1 parts, based on the 100 parts of total weight of the adhesive.

In one embodiment, the adhesive is cured through an optical clear coversheet or front sheet, and the photoinitiator must be capable ofabsorbing radiation at wavelengths for which the cover or substratesheets are transparent. For example, if an adhesive is to be curedthrough a sodalime glass coverplate, the photoinitiator must havesignificant UV absorbance above 320 nm. UV radiation below 320 nm willbe absorbed by the sodalime glass coverplate and cannot reach thephotoinitiator in the adhesive films. In this example, it would bebeneficial to include a red shifted photoinitiator, or a photosensitizerwith the photoinitiator as one photoinitiating system, to augment thetransfer of energy to the photoinitiator. If an adhesive is to be curedthrough a PET film with cut-off absorbance at 400 nm and below, thephotoinitiator must have UV absorbance above 400 nm. Examples of suchphotointiators include, but are not limited to, IRGACURE® 819, IRGACURE®2022, LUCIRIN® TPO, LUCIRIN® TPO-L, which are commercially availablefrom BASF. The range of UV radiation may be modified as necessary, andsuch modifications are within the expertise of the practitioner skilledin the art.

The term “heat cure” herein refers to toughening, hardening orvulcanization of the curable portion of the adhesive through exposure toheat in oven, infrared (IR), near IR, or microwave. The heat curetemperature is between 50-200° C., preferably 60-100° C. The initiationof the heat cure is achieved through the addition of an appropriatethermal radical initiator.

The radical initiators for heat cure include peroxides, such as,1,1,3,3-tetramethylbutyl peroxy-2-ethyl-hexanoate, 1,1-bis(t-butylperoxy) cyclohexane, 1,1-bis(t-butylperoxy)cyclo-dodecane,di-t-butyl peroxyisophthalate, t-butyl peroxybenzoate, dicumyl peroxide,t-butyl cumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane,2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne and cumene hydroperoxide.The amount of the initiator for heat cure is typically is in a range ofabout 0.001 to about 10 parts based on 100 parts of the total weight ofthe adhesive.

In one embodiment, the thermal-curing initiator is desirably selected toprovide a moderate initiation temperature, which is high enough toprevent premature cross-linking, but also low enough to prevent exposingelectronic devices to excess temperatures. Excessively high temperaturesmay degrade the reactive organic components within the devices. Examplesof suitable commercially available free radical thermal initiatorinclude, but are not limited to, LUPEROX TBEC from United Initiators,TRIGONOX 101 and TRIGONOX 201 from Akzo Nobel Polymer Chemicals, LUPEROX101 and LUPEROX 231 from Arkema, DICUP from GEO Specialty Chemicals,2,5,-Dimethyl-2,5 BIS (Tert-Butyl Peroxy) Hexyne-3, such as thoseavailable under the trade designation LUPEROX 130 from Arkema, TRIGONOX145 from Akzo Nobel Polymer Chemicals; Di-Teri-Butyl Peroxide such asthose available under the trade designation TRIGONOX B from Akzo NobelPolymer Chemicals. Typical cure temperatures for these free radicalinitiators typically range from about 80 to about 150° C., buttemperatures can be increased for faster cures.

Optionally, inorganic fillers, and desiccants may further be added tothe curable adhesive of the invention. The inorganic fillers may be usedto improve the cohesive strength, rheology, and moisture and oxygenbarrier properties of the adhesives. Representative fillers include, butare not limited to, ground quartz, fused silica, amorphous silica, talc,glass beads, graphite, carbon black, alumina, metal powders, clays,graphene, nanoclay, mica, aluminum nitride, and boron nitride. Thedesiccants may be added to the curable adhesive of the invention toimprove the moisture barrier properties of the adhesive. Arepresentative list of such desiccants can be found in Dean, J. Lange'sHandbook of Chemistry, 1999, McGraw Hill, Inc., New York, N.Y., pp.11.5. In general, suitable desiccants include metal oxides, such as,CaO, BaO, MgO; other oxides, such as SiO₂, P₂O₅, Al₂O₃; metal hydrides,such as CaH₂, NaH, LiAlH₄; metal salts, such as CaSO₄, Na₂SO₄, MgSO₄,CaCO₃, K₂CO₃, and CaCl₂; powdered zeolites, such as 4A and 3A molecularsieves; metal perchlorates, such as, Ba(ClO₄)₂, Mg(ClO₄)₂;superabsorbent polymers, such as, lightly cross linked poly(acrylicacid); and metals that react with water, such as calcium. The desiccantsare capable of reacting with, absorbing, or adsorbing water and/or watervapor.

Optionally, sliane, hydrolyzable polymeric and/or oligomeric adhesionpromoters may further be added to the curable adhesive of the invention.Examples of silane adhesion promoters that are useful include, but arenot limited to, C3-C24 alkyl trialkoxysilane,(meth)acryloxypropyltrialkoxysilane, chloropropylmethoxysilane,vinylthmethoxysilane, vinylthethoxysilane, vinyltrismethoxyethoxysilane,vinylbenzylpropylthmethoxysilane, aminopropyltrimethoxysilane,vinylthacetoxysilane, glycidoxypropyltrialkoxysilane,beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,mercaptopropylmethoxysilane, aminopropyltrialkoxysilane, and the like.However, silane adhesion promoters that reacts and degrades any activeorganic component should not be added to adhesives intended for use inelectronic device. Examples of functional polymeric and/or oligomericadhesion promoters that are useful include, but are not limited to,hydrolysable PDMS polymer or oligomer, e.g., PDMS that is endcapped withtrialkoxylsilyl (meth)acrylates, dialkoxysilyl (meth)acrylates ormethacrylates groups. The adhesion promoter will typically be used inamounts of from 0.2 to 40 weight percent, more preferably, 1 to 20weight percent of the whole curable silicone PSA. A particularlypreferred polymeric and/or oligomeric adhesion promoters ismethacryloxypropyldimethoxy terminated PDMS made by Henkel Corporation,according to U.S. Pat. No. 5,300,608. Occasionally, as known in the art,catalyst is together with the adhesion promoters for better results, intypically amounts of from 0.001 to 5 weight percent of the whole curablesilicone PSA. Examples of such catalyst that are useful include, but arenot limited to, amines, adhesion promotor catalyst and tin catalyst,e.g., dibutyltin dilaurate.

In another embodiment, the ratio of (i) the reactivepolydimethylsiloxane polymer to (ii) the reactive silicone resin to(iii) the (meth)acrylate and/or methoxyl functionalizedpolydimethylsiloxane polymer or oligomer ranges from 1:8 to 1:8 to 1:8.

The adhesives solution in the invention have a Brookfield viscosityrange of from about 100 to about 100,000 cps in the ranges of about20-40° C., preferably about 1,000 to about 10,000 cps at 25-30° C. Suchviscosity ranges allow the adhesive to be coatable into 15-250 umthickness films at ambient temperature. The viscosity is adjustable bysolid % from 20 to 80%. The adhesive solution can be coated into PSAfilms for lab testing using the solution film applicator in lab. Thecoating procedure is well-known to those skilled in the art. The PSAfilm can further be UV cured with D-bulb (Fusion Systems) with a dosageof UVA&V 1-5 J/cm², or heat cured upon heating at >80° C. for 30 min.

The PSA adhesive film has a low modulus upon UV or heat cure, especiallyin the temperature range of −40 to 80° C. Low elastic modulus indicatesthat an adhesive is soft and can easily wet-out rough substrates to fillvoids. Due to the low modulus, the adhesive film will also not imposeany Mura on an electronic display device, e.g., LCD, while significantlyimproving the performance of the display device. Mura can be minimizedif the optically clear adhesive films are soft after the cure in a widerange of temperatures. The elastic modulus measurement is well known toa person skilled in the art. The elastic modulus values recorded in thisdocument have been measured with a photorheometry or RDA. The elasticshear modulus (G′) of the cured adhesive is preferably to be less than1.0×16⁷ dyn/cm² at 20° C. and 10 rad/s after cure.

The cured silicone pressure sensitive adhesive composition is in anorganic solvent with a percent solids content of about 30 to about 80 wt%. Preferred organic solvents include aliphatic hydrocarbons, aromatichydrocarbons, diethyl ether, tetrahydrofurans.

The cured adhesive film must have good peel strength to substrates.Balance peel adhesion and soft modulus are important to avoiddelamination between adhesive layer and substrate, when flexibleelectronic devices are subject to bending, or rigid devices at verticalposition for a long period of time. The T-peel adhesion test wasperformed on Instron, in accordance with ASTM D1876, a well-knownmeasurement to a person skilled in the art. T-peel test ASTM D1876evaluates the force required to the progressively separate two bonded,flexible adherents. Variations in test specimen preparation suchadhesive curing, adhesive thickness, adherents and conditioning providesinsight for optimization in processes and application. The curedsilicone PSA of the invention preferably has T-peel adhesion of >15oz/in between PET substrates.

180 Peel adhesion can be conducted on Instron, in accordance with eitherPSTC 101 or ISO 8510 or ASTM D3330, well-known measurements to a personskilled in the art. The cured silicone PSA film of the inventionpreferably has 180 peel adhesion of >25 oz/in between PET and stainlesssteel panel.

Optical Properties (T %, haze % and yellow index b*) of the cured PSAfilm can be measured using Cary 300 from Agilent, in accordance withASTM E903 and ASTM D1003. The adhesive is considered to be opticallyclear, if the cured silicone adhesive film exhibits an opticaltransmission of at least 90%, preferably >99% between glass slides, over500-900 nm range, and with haze and yellowness b*<1%.

In one embodiment, the curable silicone PSA solution is formed by firstpreparing a reaction product of (i) a reactive α,ω-endcappedpolydimethylsiloxane polymer, (ii) a functionalized silicone resin; and(iii) an acid or a base catalyst in an organic solvent to form a solubleand non-curable silicone crosslinked network; and then combining thereaction product with (iv) 5-45% of a (meth)acrylate terminatedpolydimethylsiloxane polymer or oligomer; (v) 5-45% of a siliconeresins; (vi) 0.001-5% of a radical initiator; and (vii) optionally,0-45% of a polydimethylsiloxane polymer or oligomer.

The adhesive can be formed as a PSA film by applying the adhesivesolution onto a release liner as a coating, with a specified gram weightper square meter (GPSM), and letting the solvent evaporate in air oroven at an elevated temperature. A second release-liner is applied ontothe substantially solvent-free PSA film, to form a laminate PSA film inbetween the two release liners. Exemplary release liners include PETfilm, Kraft paper with fluoro-silicone release coatings.

The curable silicone PSA film can be delivered as an uncured film, asbeing called UV curable optically clear film (UVOCA); or heat curableoptically clear film (HOCA). Furthermore, the curable silicone PSA filmcan be delivered as a fully cured film, as being called optically clearfilm (OCA). The recommended cure condition is either by UV with a dosageof UV 1-5 J/cm², or upon heating at >80° C. The silicone PSA film canwithstand shipping and storage temperatures under stress. This PSA filmmaintains pressure sensitivity at or below −40° C. and with minimal orzero cold flow in storage. The sheets and rolls can later be die cutinto desirable sizes and shapes.

The electronic device utilizing the inventive silicone PSA film isassembled in various ways. In one embodiment, the PSA film is placed inbetween the two release liner substrates as described above, and onerelease liner is removed. The exposed adhesive film is laminated toeither the front cover sheet or the back substrate of the device.Subsequently, the other release liner is removed from the PSA film andthe exposed adhesive surface is then laminated to the remaining frontsheet or the substrate. Lamination process, with a rubber rollerlaminator, under pressure in autoclave, heat and/or vacuum may be usedto enhance lamination and avoid voids or trapping air. If PSA film isnot cured as in the form of UVOCA or HOCA, the laminated device shouldthen subject to cure with UV irradiation or heating to crosslink the PSAfilm and securely adheres the front cover sheet to the back substrate.

In another embodiment, the adhesive film is laminated to both frontcover sheet and the back substrate simultaneously. Heat with temperatureranging from about 40° C. to about 150° C. Vacuum and/or pressure can beapplied to enhance lamination and to remove any entrapped air (voids)between the layers. Preferably, the laminating temperature is belowabout 110° C., and in some application below about 80° C. becauseorganic active components in the electronic devices may decompose attemperatures above 120° C. If PSA film is not cured as in the form ofUVOCA or HOCA, the laminated device should then subject to cure with UVirradiation or heating to crosslink the PSA film and securely adheresthe front cover sheet to the back substrate.

UV cure is completed by exposing the adhesive film to UV light sourcehaving a wavelength of about 280 to about 700 nm, with a dosage of about1-5 J/cm². Heat cure is completed at heating at temperatures of fromabout >80° C., preferably at 120° C. over a period of time.

In another embodiment, the adhesive is first cured and then laminatedonto the front cover sheet and the back substrate. The cured pressuresensitive adhesive film still has enough tack and grab and adheres ontothe substrates.

In yet another embodiment, the adhesive film of the invention may be ina single layer or in a multilayer form in the device. The single layerfilm refers to the adhesive described in the invention as the sole andonly film to adhere the cover and the substrate together. For multilayerform, at least one of the layers is the adhesive described in theinvention, and the device further includes other layer(s) that may bemade of other suitable substrate or polymeric material(s), for example,copolymers of α-olefins and α,ω-ethylenically unsaturated carboxylicacids (i.e., acid copolymers), p artially neutralized ionic acidcopolymers (i.e., ionomers), ethylene/vinyl acetate copolymers,polyvinyl acetals) (including acoustic grade polyvinyl acetals),polyurethanes, polyvinylchlorides, polyethylenes (e.g., linear lowdensity polyethylenes), polyolefin block copolymer elastomers,copolymers of α-olefins and α,ωethylenically unsaturated carboxylic acidesters (e.g., ethylene methyl acrylate copolymers and ethylene butylacrylate copolymers), silicone elastomers, epoxy resins, andcombinations thereof.

The curable adhesive of the invention is useful for display devices thatrequires optical clarity and/or touch sensory.

In one embodiment, the curable adhesive described herein is useful asoptically clear adhesive (OCA) or ultra-violet curable optically clearadhesive (UVOCA) film for bonding optical assemblies. The term OCA andUVOCA is well established in the art. The OCA and UVOCA film bonds thecover lens, plastic or other optical materials to the display modulesubstrate. OCA and UVOCA are generally used to improve the opticalcharacteristics of the device, including minimizing Mura, as well as toimprove durability and process efficiency. Major applications of OCA andUVOCA include capacitive touch panels, LED/OLED televisions.

In one particular embodiment, the curable silicone PSA film of theinvention is particularly useful as OCA or UVOCA for flexible andfoldable display devices that requires resistance to folding and bendingcurvature.

There are several ways to incorporate the OCA or UVOCA film of theinvention between the cover lens and the display module substrate in theLCD, LED, touch panel display devices. The OCA or UVOCA film of theinvention is preferably applied on the cover lens. The OCA or UVOCA filmis typically protected between two release liners, the first liner isthinner (25-50 μm) and easier to remove, and the other is thicker(75-100 μm) and has higher release force. The OCA or UVOCA film, afterthe first liner is removed, is applied onto the cover lens by pressingand laminating in one direction by a rubber roll. The second releaseliner is then removed and the exposed surface of the adhesive film islaminated unto the display module substrate, preferably under vacuum(<0.1 MPa) and/or pressure in autoclave (<0.5 MPa). Vacuum condition ispreferred for a bubble-free bonding. Heating may also be applied,preferably in the rage of about 40 to about 80° C.

The UVOCA of the invention is cured through the top substrate byexposure to electromagnetic irradiation comprising a wavelength rangingfrom 200 nm to 700 nm, preferably from 450 nm to 500 nm. The curingdegree can be determined by measuring the decrease of the IR absorptionat an absorption peak which is characteristic to the correspondingformulation chemistry. This is well established to the person skilled inthe art. UV-irradiation can be supplied with a continuous high intensityemitting system, such as those available from Fusion UV Systems. A metalhalide lamp, LED lamp, high-pressure mercury lamp, xenon lamp, Xenonflash lamp etc. can be used for UV cure, with an energy range of about 1to about 5 J/cm².

In a preferred embodiment, the top substrate is selected from glass orpolymer film, preferably plastic films, including in particularpolyethylene terephthalate, polymethyl(meth)acrylate, polyimide film,and/or triacetate cellulose (TAC). In another preferred embodiment, thetop substrate is a reflector, cover lens, touch panel, retarder film,retarder glass, LCD, lenticular lens, mirror, anti-glare oranti-reflective film, anti-splinter film, a diffuser or anelectromagnetic interference filter. For example for 3D TV applications,a glass or film retarder will be bonded onto a LCD for passive 3D TV, ora TN LCD or lenticular lens is bonded a regular TFT LCD for naked eye3D. The base substrate is a LCD module with polarizer film on top. Thebase substrate can be a display panel, preferably selected from a liquidcrystal display, a plasma display, a light-emitting diode (LED) display,an electrophoretic display, and a cathode ray tube display.

Yet in another embodiment, the display panel has a touch functionality.The adhesive of the invention and the application process of theinvention can be used for any touch panel sensor assembly. The adhesiveof the invention can be used to bond touch panel sensors that requiretwo layers of indium-tin-oxide coated glass. The adhesive can be usedfor cover lens bonding, in particular to fill the air gap in touch panelsensors that utilize a cover lens, such as clear plastic polymethyl(meth)acrylate, and the glass touch panel sensor. The adhesive can beused for directly bonding the cover lens to a LCD module. In anotherembodiment, the invention comprises the possibility of two or more topsubstrates bonded one after another onto a base substrate with the OCAor UVOCA of the invention between layers.

In one embodiment, the curable adhesive is useful as an encapsulant forflexible photovoltaic module/cell (interchangeably used herein). Thephotovoltaic module assembly includes any article or material that canconvert light into electrical energy. In forming the photovoltaic cell,the encapsulant sheet or roll, comprising the curable adhesive film, islaminated to the photovoltaic module assembly. The flexible photovoltaiccell, including the encapsulant, must be sufficiently transparent toallow adequate sunlight or reflected sunlight to reach the photovoltaiccells and withstand folding and bending curvature during its usage.

The curable adhesive is reworkable. If a defect is found in anelectronic device, the film can be readily removed from either the coversheet or the substrate. The adhesive film remains as a single, solidpiece or breaks into few pieces that can be removed without any solventor without damaging the other components in the device. The cover sheetand the substrate can be reused with another adhesive film to formanother electronic device.

Many modifications and variations of this invention can be made withoutdeparting from its spirit and scope, as will be apparent to thoseskilled in the art. The specific embodiments described herein areoffered by way of example only, and the invention is to be limited onlyby the terms of the appended claims, along with the full scope ofequivalents to which such claims are entitled.

EXAMPLES

Elastomer 50N (Mw 110000 g/mol) is a silicone polymer, commerciallyavailable from Wacker.

PDMS-DA is methacryloxypropyldimethoxy terminated polydimethylsiloxane,commercially available from Henkel.

MQ is a hydroxyl functional silicone resin (Mw ˜9000 g/mol) commerciallyavailable from Dow Corning, Momentive and Wacker.

Heptane, ammonium carbonate, n-butyl lithium (1.6M in hexane) (nBuLi),potassium hydroxide (1.0N water solution) are commercially availablefrom Aldrich.

TPO is a photoinitiator, commercially available from BASF.

Tests Temperature Sweep Test:

A Rheometrics Dynamic Mechanical Analyzer (Model RDA 700) was used toobtain the elastic moduli (G′), loss modulus (G″) and tan delta versustemperature sweep. The instrument was controlled by Rhios softwareversion 4.3.2. Parallel plates 8 mm in diameter and separated by a gapof about 2 mm were used. The sample was loaded and then cooled to about−100° C. and the time program started. The program test increased thetemperature at 5° C. intervals followed by a soak time at eachtemperature of 10 seconds. The convection oven was flushed continuouslywith nitrogen. The frequency was maintained at 10 rad/s. The initialstrain at the start of the test was 0.05% (at the outer edge of theplates). An autostrain option in the software was used to maintain anaccurately measurable torque throughout the test. The option wasconfigured such that the maximum applied strain allowed by the softwarewas 80%. The autostrain program adjusted the strain at each temperatureincrement if warranted using the following procedure. If the torque wasbelow 200 g-cm the strain was increased by 25% of the current value. Ifthe torque was above 1200 g-cm it was decreased by 25% of the currentvalue. At torques between 200 and 1200 g-cm no change in strain was madeat that temperature increment. The shear storage or elastic modulus (G′)and the shear loss modulus (G″) are calculated by the software from thetorque and strain data. Their ratio, G″/G′, also known as the tan delta,was also calculated. The soft block Tg was taken as the maximum in tandelta. Flow temperature was reported as the temperature where elasticmodulus and loss modulus values equal to one another: G″=G′.

T-Peel Test:

The T-peel adhesion test was performed on Instron Sintech 1/D, inaccordance with ASTM D1876. The procedure was as follows: (1) transferadhesive films to between two 2-3 mil PET films; (2) UV cure thelaminated adhesive with D-bulb (Fusion Systems) with a dosage of UVA&V1-5 J/cm²; (3) cut specimens to 1.0 in wide×6-12 in long strips; (4)condition at 23° C. and 50% relative humidity for 12 hr; (5) perform theT-peel adhesion at 23° C. and 50% relative humidity: clamp each ends ofthe t-peel specimen in separate test grips of the Instron at a rate of12.0 in/min) length of the bond line.

Transmission Test:

Optical properties (T %, haze % and yellow index b*) were measured witha spectrometer, Cary 300 from Agilent, in accordance with ASTM E903 andASTM D1003. Preferred testing method for transmission was as follows:(1) place a small film of adhesive on a 75 mm by 50 mm plain micro slide(a glass slide from Dow Corning, Midland, Mich.), that had been wipedthree times with isopropanol; (2) attach a second glass slide onto theadhesive under a force; (3) cure the adhesive with a D-bulb (FusionSystems) at UVA&V 1-5 J/cm²; and measure the optical transmission from300 to 900 nm with the spectrometer.

Example 1

A mixture of polydimethylsiloxane polymer (Wacker Elastomer 50N, 15 g),hydroxyl MQ resin (33 g), (NH₄)₂CO₃ (0.3 g), and heptane (60 g) wasstirred at 60° C. for 2 hr. The reaction mixture was then heated toreflux of heptane for 2 hours, with a slow N₂ purge. The product wascooled to room temperature and packed in a glass jar.

Examples 2-6

Examples 2-6 were made by combining additional components to Example 1,as set forth in Table 1.

TABLE 1 Examples 1 2 3 4 5 6 Components Example 1, g 10 10 10 10 10 10PDMS-DA, g NA 2.5 2.5 2.5 2.5 2.5 MQ, g NA 2.5 3.5 5.5 7.0 8.5 Elastomer50N, g NA 0 0 0 0 0 TPO, g NA 0.05 0.05 0.05 0.05 0.05 PropertiesT-Peel, oz/in 29 20 28 31 29 26 G′, ×10⁵ dyn/cm², −40° C. 5670 5690 62006710 6970 7370 G′, ×10⁵ dyn/cm², 20° C. 320 440 740 980 1160 2040 G′,×10⁵ dyn/cm², 80° C. 0.8 1.9 2.2 3.2 5.8 23

As shown in Table 1, adding more MQ led to higher T-peel values andhigher shear modulus G′ values.

Example 7

A mixture of polydimethylsiloxane polymer (15 g), hydroxyl MQ resin (33g), and heptane (60 g) was stirred at reflux for 2 hours, with N₂ gasblanket. Catalyst nBuLi (0.3 mL, 1.6M in hexane) and was added and themixture was mixed for an additional one hour. The reaction mixture waspurged with CO₂ for 1 hour, followed by N₂ for 1 hour. The product wascooled to room temperature and packed in a glass jar.

Examples 8-15

Examples 8-15 were made by combining additional components to Example 7,as set forth in Table 2.

TABLE 2 Examples 7 8 9 10 11 12 13 14 15 Components Example 7, g 10 1010 10 10 10 10 10 10 PDMS-DA, g NA 2.5 2.5 2.5 2.5 2.5 3 3 3 MQ, g NA2.5 3.5 5.5 7.0 8.5 0 1 2.5 Elastomer 50N, g NA 0 0 0 0 0 1 0 0 TPO^(d),g NA 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Properties T-Peel, oz/in 2724 29 31 33 31 15 22 31 G′, ×10⁵ dyn/cm², −40° C. 6490 6740 7320 79409050 9940 430 1380 3990 G′, ×10⁵ dyn/cm², 20° C. 670 890 970 1130 12801460 8.4 24 110 G′, ×10⁵ dyn/cm², 80° C. 2.8 3.1 4.1 4.6 5.4 6.1 1.8 2.73.2

Products from n-butyl lithium reaction have higher T-peel adhesion andless modulus G′ variation over the temperature range of −40 to 80° C.,compared to the adhesives made with ammonium carbonate catalyst. Asshown in Table 3, adding more MQ led to higher T-peel and higher shearmodulus G′.

Example 13-14 have a good balance of T-peel adhesion and low modulus inthe entire temperature range of 40 to 80° C., in comparison to Examples7-12 (FIG. 1). Other mechanical and optical properties are showed inTable 3. The entire RDA temperature sweep tests of Examples 12 and 13are shown in FIG. 1.

TABLE 3 Examples 13 14 15 Elongation at break, % >1500 >1500 >1500 180Peel at 1 mil, oz/in 26 35 50 180 Peel at 2 mil, oz/in 41 53 72 T %,between 1 mm glasses >99% >99% >99% Haze, % <0.5 <0.5 <0.5 b*, % <0.2<0.2 <0.2

Examples 16-17

The reaction conditions for the reacted portion of Example 16 was madesimilar to Example 1. The reaction portion of Example 17 was made bymaking a mixture of polydimethylsiloxane polymer (Elastomer 50N, 20 g),hydroxyl MQ resin (30 g), methacryloxypropyldimethoxy terminatedpolydimethylsiloxane (10 g), KOH solution (1.0N, 0.05 g), and heptane(50 g) was stirred at 60° C. for 2 hr. The reaction mixture was purgedwith CO₂ for 1 hour, and followed by N₂ for 1 hour. TPO (0.05 g) wasadded and mixed for 30 minutes. The product was cooled to roomtemperature and packed in a glass jar.

TABLE 4 Examples 16 17 Reaction product PDMS-DA, g 31 31 MQ, g 69 69Catalyst, g or mL (NH₄)₂CO₃ 0.3 g KOH 0.05 g Further combined with MQ, g10 10 PDMS-DA, g 30 30 TPO, g 0.5 0.5 Properties T-Peel, oz/in 2.4 20G′, ×10⁵ dyn/cm², −40° C. 1350 1210 G′, ×10⁵ dyn/cm², 20° C. 4.2 11 G′,×10⁵ dyn/cm², 80° C. <0.001 1.5

Example 16 was a weak film with low T-peel and modulus at 80° C. Example17 had similar T-peel as Example 14, however, it gelled in solution instorage within one week.

Many modifications and variations of this invention can be made withoutdeparting from its spirit and scope, as will be apparent to thoseskilled in the art. The specific embodiments described herein areoffered by way of example only, and the invention is to be limited onlyby the terms of the appended claims, along with the full scope ofequivalents to which such claims are entitled.

We claim:
 1. A curable silicone pressure sensitive adhesive compositioncomprising a mixture of: (a) about 10-to about 98% of a reaction productconsisting of (i), (ii), and (iii), wherein; (i) a reactivepolydimethylsiloxane polymer; (ii) a reactive silicone resin; and (iii)an acid or a base catalyst that has a pKa value equal to or less than −6or equal to or greater than 15; (b) about 1 to about 45% of a terminalor pendant (meth)acrylate functionalized polydimethylsiloxane polymer oroligomer; (c) about 1 to about 45% of a silicone resin or apolydimethylsiloxane polymer or oligomer; and (d) about 0.001 to about5% of a radical initiator; and wherein the cured adhesive has atransmittance, measured in accordance with ASTM E903 at 500 nm, ofgreater than 90%.
 2. The curable silicone pressure sensitive adhesivecomposition of claim 1, wherein the ratio of the reactivepolydimethylsiloxane polymer (i) to the reactive silicone resin (ii)ranges from 1:9 to 9:1.
 3. The curable silicone pressure sensitiveadhesive composition of claim 1, wherein the reactivepolydimethylsiloxane polymer (i) is α,ω-endcapped with hydroxyl and/oralkoxy group.
 4. The curable silicone pressure sensitive adhesivecomposition of claim 1, wherein the reactive silicone resin consists oftetrafunctional siloxyl units (SiO_(4/2)) and triorganosiloxy units(R₃SiO_(1/2)), wherein the R is hydroxyl group and methyl group, whereinthe mole ratio of the units of the SiO_(4/2) to the R₃SiO_(1/2) is from1:2 to 2:1, and wherein the weight average molecular weight of thereactive silicone resin is from about 500 to 200,000 g/mol.
 5. Thecurable silicone pressure sensitive adhesive composition of claim 1,wherein the catalyst is selected from the group consisting KOH, NaOH,LiOH, organolithium reagents, Grignard reagents, methanesulfonic acid,sulfuric acid, and mixtures thereof.
 6. The curable silicone pressuresensitive adhesive composition of claim 1, wherein the reaction productis formed in an organic solvent selected from the group consisting ofaliphatic hydrocarbons, aromatic hydrocarbon, diethyl ether,tetrahydrofuran, and mixtures thereof.
 7. The curable silicone pressuresensitive adhesive composition of claim 1, wherein the (meth)acrylatefunctionalized polydimethylsiloxane polymer or oligomer is an PDMSpolymer or oligomer α,ω-endcapped with an acrylate or a methacrylatefunctional group, having a weight average molecular weight of about 400to 350,000 g/mol.
 8. The curable silicone pressure sensitive adhesivecomposition of claim 1, wherein the silicone resin (c) consists oftetrafunctional siloxyl units (SiO_(4/2)) and triorganosiloxy units(R₃SiO_(1/2)), wherein the R is independently, methyl, hydroxyl,hydride, vinyl, (meth)acryloxy functional group, or mixtures thereof,wherein the mole ratio of the SiO_(4/2) to the R₃SiO_(1/2) unit is from1:2 to 2:1, and wherein the weight average molecular weight of fromabout 500 to 200,000 g/mol.
 9. The curable silicone pressure sensitiveadhesive composition of claim 1, wherein the polydimethylsiloxanepolymer or oligomer (c) is an PDMS polymer or oligomer α,ω-endcappedwith independently, methyl, hydroxyl, H, vinyl, (meth)acryloxyfunctional group, or mixtures thereof, and the weight average molecularweight of from about 400 to 350,000 g/mol.
 10. The curable siliconepressure sensitive adhesive composition of claim 1, wherein the radicalinitiator (d) is a UV cleavable photoinitiator.
 11. The curable siliconepressure sensitive adhesive composition of claim 1, optionally comprisesa silane adhesion promoter, hydrolyzable PDMS polymer, hydrolysable PDMSoligomer, amine adhesive promotor catalyst or a tin catalyst.
 12. Thecurable silicone pressure sensitive adhesive composition of claim 1,further comprising a plurality of inorganic fillers or desiccants.
 13. Amethod of forming an electronic device comprising the steps of: (1)making the curable silicone pressure sensitive adhesive composition ofclaim 1, (2) coating the curable silicone pressure sensitive adhesivecomposition in between two release-liners; (3) preparing a firstsubstrate, wherein the substrate can be a front cover sheet or a backsubstrate of a first device substrate; (4) removing one release-liner;(5) laminating the curable silicone pressure sensitive adhesivecomposition onto the first device substrate at a pressure of about 0.01to about 0.5 MPa; (6) removing the other release-liner; (7) laminatingthe curable silicone pressure sensitive adhesive film onto a seconddevice substrate at a pressure of about 0.01 to about 0.5 MPa; and/or avacuum of about 0.01 to about 0.1 MPa, and/or at a temperature of about30 to 80° C.; (8) curing the curable silicone pressure sensitiveadhesive film with a dosage of UVA&V 1-5 J/cm², and/or heat at 80-150°C.; whereby the adhesive film adheres onto the first device and thesecond device substrates.
 14. A method of forming an electronic devicecomprising the steps of: (1) making the curable silicone pressuresensitive adhesive composition of claim 1, (2) coating the curablesilicone pressure sensitive adhesive composition in between tworelease-liners; (3) preparing a first substrate, wherein the substratecan be a front cover sheet or a back substrate of a first devicesubstrate; (4) removing one release-liner; (5) laminating the curablesilicone pressure sensitive adhesive composition onto the first devicesubstrate at a pressure of about 0.01 to about 0.5 MPa; (6) removing theother release-liner; (7) laminating the curable silicone pressuresensitive adhesive film onto a second device substrate at a pressure ofabout 0.01 to about 0.5 MPa; and/or a vacuum of about 0.01 to about 0.1MPa, and/or at a temperature of about 30 to 80° C. (8) curing thecurable silicone pressure sensitive adhesive film with a dosage of UVA&V1-5 J/cm², and/or heat at 80-150° C.; whereby the adhesive film adheresonto the first device and the second device substrates.